By Agence France-Presse The World Health Organization (WHO) said Thursday that a few hundred million COVID-19 vaccine doses could be produced by the end of the year – and be targeted at those most vulnerable to the virus. The UN health agency said it was working on that assumption, with a view to two billion doses by the end of 2021, as pharmaceutical firms rush to find a vaccine. WHO chief scientist Soumya Swaminathan said researchers were working on more than 200vaccine candidates around the world, including 10 that are in human testing. “If we’re very lucky, there will be one or two successful candidates before the end of this year,” she told a virtual press conference. She identified three groups most in need of the first wave of vaccine doses. They are front-line workers with high exposure, such as medics and police officers; those most vulnerable to the disease, such as the elderly and diabetics; and people in high-transmission settings, such as urban slums and care homes. “You have to start with the most vulnerable and then progressively vaccinate more people,” Swaminathan said. “We are working on the assumption that we may have a couple of hundred mil - lion doses at the end of this year, very optimistically,” she said. “We’re hoping that in 2021 we will have two billion doses of one, two or three effective vaccines to be dis - tributed around the world. But there’s a big ‘if’ there, because we don’t yet have any vaccine that’s proven. “But because of all the investments going into this, let’s say we have two billion doses by the end of 2021 – we should be able to vaccinate at least these priority populations.” Pharmaceutical compa - ny executives said late last month that one or several COVID-19 vaccines could be - gin rolling out before 2021, but warned that an estimated total of 15 billion doses would be needed to suppress the virus. Swaminathan said scien - tists were analyzing 40,000 sequences of the new coro - navirus and while all viruses mutate, this one was doing so far less than influenza, and had not yet mutated in the key areas that would alter the severity of disease or the immune response. Lower immunity People who catch COVID19 but don’t show symptoms may have significantly lower levels of immunity against the virus than those who become severely ill, new research showed Thursday. The majority of virus pa - tients display relatively minor signs of infection, and a small proportion show no symptoms at all. Very little is known about this group, given that they are far less likely to be tested than those who go on to develop severe symptoms including respiratory problems. Researchers based in Chi - na compared two groups of individuals infected with COVID-19 in Chongqing’s Wanzhou district: 37 who showed symptoms versus 37 who did not. The researchers analyzed blood samples from both groups taken a few weeks after recovering and found that just 62.2 percent of the asymptomatic group had short-term antibodies, com - pared with 78.4 percent of symptomatic patients. After eight weeks of con - valescence, antibody pres - ence had fallen in 81.1 percent of asymptomatic patients, compared with 62.2 percent of symptomatic patients. What’s more, asymp - tomatic patients were found to have lower levels of 18 pro- anti-inflammatory cellsignaling proteins than the symptomatic group, suggesting a weaker immune response to the novel coronavirus. Authors of the study, which was published in Na - ture Medicine, said their findings called into question the idea that everyone who has had coronavirus are im - mune to future infection. “These data might indi - cate the risks of using COVID19 ‘immunity passports’ and support the prolongation of public health interventions, including social distancing, hygiene, isolation of highrisk groups and widespread testing,” they wrote. Danny Altmann, a spokes - man for British Society for Immunology as well as pro - fessor of Immunology at Imperial College London, said the research raised a vital question for combating COVID-19. “Much immunology data so far has come from analyz - ing the sickest, hospitalized patients, but most people who have been more mildly affected will want to know whether this is likely to have conferred lasting, protective immunity,” he said. Altmann said it was “an important and potentially worrying point” that many patients in the study showed a significant decline in antibody levels in just two months. “Though this is quite a small sample size of patients, it is in line with some con - cerns that natural immunity to coronaviruses can be quite short-lived,” said Altmann, who was not involved in the research.